Sky & Telescope - April 2019 - 58

APRIL 2019 OBSERVING
Going Deep

γ

β

μ

NGC 4565

ε

ζ

NGC 2903
Algieba

M64

η

M85

α
M53

Regulus

N

N

p Left: This sketch of galactic cirrus in the Sickle of Leo is a mosaic of several drawings resulting from several "sweeps" of the telescope across the
area. Right: This mosaic of the Coma Berenices region features not only galactic cirrus but also the tight globular cluster M53 and several galaxies.

as 2-3% contrast, given good object
composition in the field of view.
I find that 100° apparent field-ofview eyepieces operated at maximum eye
pupil of 5-7 mm are the best for detecting galactic cirrus. Consequently, I use
very fast mirrors, f/2.6 to f/3.0, so as to
achieve the desired pupil size. The resulting fields of view are eye-opening: 4.2°
for the 6-inch f/2.8, 2.4° for the 10.5inch f/2.7, 1.8° for the 13.2-inch f/3.0,
and 1.1° for the 25-inch f/2.6. Not only
is the face-on spiral galaxy M101 a wonderful view at low power in the 25-inch,
with the spiral arms embedded in the
glow of the galaxy, but there's an arc of
the Milky Way's galactic cirrus at the
edge of the field almost touching NGC
5474. At the same time, the smaller
galaxies NGC 5485, NGC 5473, and
NGC 5422 are visible. All this makes for
an interesting effect, in which the view
through the eyepiece appears flat yet my
brain is telling me that the cirrus and
galaxies form an immensely deep 3D
view. I found myself staring at the field
for a long time, unable to move to my
next object. This leaves a visual memory
and emotional astonishment that I can
recall by looking at my drawing.
I've begun stitching together fields
of view to form sketching mosaics. I'll
58

A PR I L 2 019 * SK Y & TELESCOPE

move the scope back and forth across
several fields of view, then pencil in
what I see. From the end point, I'll
begin another sweep. I'll then sweep
all the way back to the very first field
of view and repeat the sweeps one after
the other until I build up a view up to
100 square degrees. I'll usually go back
a second or third night to confirm the
sketch as well as tie up loose ends that I
failed to knot the first time. The image
of galactic cirrus in the Sickle of Leo
with the pretty galaxy NGC 2903 above
is a mosaic of several drawings, each
drawing stretching over multiple fields
of view. Luckily it's hard to get lost in
Leo's sickle with its prominent guide
stars. Another mosaic of the Coma
Berenices region not only features the
galaxies NGC 4565, M85, and M64, but
also the tight globular cluster M53.
Comparing with views through other
amateur telescopes, I've found that
extraordinarily wide apparent fields
of view, dark skies, knowing what to
expect at the eyepiece, and enhanced
coatings all make a difference. Experience also helps significantly: I see
galactic cirrus much more easily now
after three years of thorough searching
and observing. Filters don't help much
- only rarely have I used a narrow

bandpass filter to increase contrast in
certain views. Surprisingly, aperture
doesn't have much impact - if anything, smaller to medium aperture
is often better.
At right is a comparison of M51,
the Whirlpool Galaxy, in three telescopes where the aperture doubles, then
doubles again: a 6-inch, a 13.2-inch,
and a 25-inch. Note that the 6-inch
detects a broader area of galactic cirrus
but lacks detail near the galaxy itself.
The 13.2-inch and 25-inch views are
very similar, differing only in image
scale, with the galactic cirrus perceived
as equally bright in both telescopes. The
view in the 6-inch stretches all the way
to M63, whereas the view in the 25-inch
has enough room for a large M51 and
the crisscrossing galactic cirrus of the
Milky Way even at low power. All three
views through the eyepiece astonish me
equally - I cannot pick a favorite.
Dwarf galaxies are a good match for
galactic cirrus in that they are approximately the same brightness. Curiously,
to my eye there's a difference in hue.
Sometimes I'll see the galactic cirrus
before I detect the dwarf galaxy - this
is the case with the Draco Dwarf
Galaxy. In fact, on occasion I'll trace
my way to the dwarf galaxy by follow-



Sky & Telescope - April 2019

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Sky & Telescope - April 2019 - 1
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